Energy, work and power — practice question

A plane makes an angle of $\sin^{-1}\!\left(\tfrac{1}{8}\right)$ with the horizontal. $A$ and $B$ are two points on the same line of steepest descent, with $A$ lying above $B$. The length $AB$ is $12\,\text{m}$. A small object $P$ of mass $8\,\text{kg}$ is released from rest at $A$ and slides down the plane, reaching $B$ with speed $4.5\,\text{m s}^{-1}$. For the motion of $P$ from $A$ to $B$, determine